Hollow drive shaft for vehicle and manufacturing method thereof

ABSTRACT

A method of manufacturing a hollow drive shaft for a vehicle may include swaging one of a first hollow tube and a second hollow tube having a same diameter to reduce an outer diameter thereof and thus allow the swaged hollow tube to be assembled in a remaining hollow tube of the first hollow tube and the second hollow tube, assembling the hollow tube that is reduced in outer diameter in the remaining hollow tube, thereby forming a hollow shaft, and joining first and second sterns to both sides of the hollow shaft, respectively.

CROSS-REFERENCE(S) TO RELATED APPLICATION

The present application claims priority to Korean Patent ApplicationNumber 10-2015-0052117 filed Apr. 14, 2015, the entire contents of whichis incorporated herein for all purposes by this reference.

BACKGROUND OF THE INVENTION Field of the Invention

The present invention relates to a hollow drive shaft for a vehicle anda manufacturing method thereof. More particularly, the invention relatesto a hollow drive shaft for a vehicle and a manufacturing methodthereof, which are intended to improve durability by enhancing physicalproperties without an increase in size.

Description of Related Art

Generally, a vehicle is equipped with a drive shaft to transmit power ofan engine from a transaxle to left and right wheels of the vehicle, thetransaxle being driven by power shift from a transmission.

The drive shaft is configured to be connected between a fixed centertype constant velocity joint coupled to the left and right wheels and aslidable constant velocity joint coupled to the transaxle, thustransmitting power from the transaxle to the left and right wheels ofthe vehicle and thereby allowing the vehicle to be driven.

FIG. 1 is a sectional view schematically showing a conventional hollowdrive shaft for a vehicle.

As shown in FIG. 1, the conventional hollow drive shaft includes ahollow shaft 1 that is provided on a central region thereof and has ahollow portion 4 extending in a direction of a rotation axis, and firstand second stems 2 and 3 that are welded to both sides of the hollowshaft 1, respectively.

The conventional hollow drive shaft is made by joining the hollow shaft1 at the central region to the stems 2 and 3 on both sides through afriction welding method in which parts (i.e. the hollow shaft and thefirst and second stems) are welded with pressure using frictional heatgenerated during the relative rotation of the welded parts.

Such a hollow drive shaft is higher in rigidity and strength compared toa solid drive shaft simply having a solid portion without having ahollow portion at the central region, thus leading to an increase innatural frequency. Consequently, the hollow drive shaft advantageouslypermits a damper to be eliminated, in addition to reducing a weight.

The damper is sensitive to temperature change and is deteriorated inperformance for several reasons, such as rubber curing, over time. Thus,in the conventional hollow drive shaft, the elimination of the dampermay cause several problems.

Meanwhile, an internal-combustion-engine vehicle performs forwardmovement rather than rearward movement and does not perform regenerativebraking, so that the drive shaft is mainly driven under aunidirectional-movement condition in which torsion torque is applied inthe forward movement direction of the vehicle. In contrast, in aneco-friendly vehicle performing the regenerative braking, such as ahybrid vehicle or an electric vehicle, the drive shaft is driven under abidirectional-movement condition in which the torsion torque is appliedin the forward movement direction of the vehicle at the time of thetravel but is applied in the rearward movement direction of the vehicleat the time of the regenerative braking.

Therefore, if the hollow drive shaft, which does not consider thebidirectional-movement condition required for the eco-friendly vehicle,is mounted to the eco-friendly vehicle, durability is poor in thebidirectional movement and thereby the drive shaft may be undesirablydamaged.

In order to solve the problem where such a drive shaft is damaged, amethod of increasing the size of the drive shaft has been conventionallyproposed. However, this may lead to an increase in diameter of the driveshaft, so that it is disadvantageous in terms of a layout.

The information disclosed in this Background of the Invention section isonly for enhancement of understanding of the general background of theinvention and should not be taken as an acknowledgement or any form ofsuggestion that this information forms the prior art already known to aperson skilled in the art.

BRIEF SUMMARY

Various aspects of the present invention are directed to providing ahollow drive shaft for a vehicle and a manufacturing method thereof,which are intended to improve durability by enhancing physicalproperties without an increase in size of the drive shaft.

Further, various aspects of the present invention are directed toproviding a hollow drive shaft for a vehicle and a manufacturing methodthereof, which are enhanced in bidirectional-movement durability to copewith an external force exerted from an outside in thebidirectional-movement condition of an eco-friendly vehicle.

According to various aspects of the present invention, a method ofmanufacturing a hollow drive shaft for a vehicle may include swaging oneof a first hollow tube and a second hollow tube having a same diameterto reduce an outer diameter thereof and thus allow the swaged hollowtube to be assembled in a remaining hollow tube of the first hollow tubeand the second hollow tube, assembling the hollow tube that is reducedin outer diameter in the remaining hollow tube, thereby forming a hollowshaft, and joining first and second stems to both sides of the hollowshaft, respectively.

The method may further include applying torsion torque to the first andsecond hollow tubes in different directions, respectively, between theswaging and the assembling.

The method may further include applying torsion torque to the first andsecond hollow tubes in different directions, respectively, between theassembling and the joining.

The method may further include applying torsion torque to one of thefirst and second hollow tubes, between the swaging and the assembling.

The method may further include applying torsion torque to one of thefirst and second hollow tubes, between the assembling and the joining.

The method may further include applying torsion torque to the first andsecond hollow tubes in a same direction, respectively, between theswaging and the assembling.

The method may further include applying torsion torque to the first andsecond hollow tubes in a same direction, respectively, between theassembling and the joining.

According to various aspects of the present invention, a hollow driveshaft for a vehicle may include a hollow shaft, and first and secondstems joined to left and right sides of the hollow shaft, in which thehollow shaft may be configured such that one of a first hollow tube anda second hollow tube is inserted into a remaining hollow tube of thefirst hollow tube and the second hollow tube.

The hollow shaft may be formed by reducing an outer diameter of one ofthe first and second hollow tubes having a same diameter throughswaging, and then inserting the hollow tube having the reduced outerdiameter into the remaining hollow tube.

One of the first and second hollow tubes may be subjected to swaging,such that an outer diameter thereof is reduced to be less than an innerdiameter of the remaining hollow tube, and then torsion torque isapplied to the first and second hollow tubes, respectively, in differentdirections to be twisted.

The hollow shaft may have therein a hollow portion extending along arotation axis, each of the first and second stems having a solid shapehaving no hollow portion therein or having a hollow shape that extendsalong the rotation axis.

It is understood that the term “vehicle” or “vehicular” or other similarterms as used herein is inclusive of motor vehicles in general such aspassenger automobiles including sports utility vehicles (SUV), buses,trucks, various commercial vehicles, watercraft including a variety ofboats and ships, aircraft, and the like, and includes hybrid vehicles,electric vehicles, plug-in hybrid electric vehicles, hydrogen-poweredvehicles and other alternative fuel vehicles (e.g., fuel derived fromresources other than petroleum). As referred to herein, a hybrid vehicleis a vehicle that has two or more sources of power, for example, bothgasoline-powered and electric-powered vehicles.

The methods and apparatuses of the present invention have other featuresand advantages which will be apparent from or are set forth in moredetail in the accompanying drawings, which are incorporated herein, andthe following Detailed Description, which together serve to explaincertain principles of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a sectional view schematically showing a conventional hollowdrive shaft for a vehicle according to the related art.

FIG. 2 is a sectional view schematically showing an exemplary hollowdrive shaft for a vehicle according to the present invention.

FIG. 3 is a schematic view sequentially showing steps of a method ofmanufacturing an exemplary hollow drive shaft for a vehicle according tothe present invention.

FIG. 4 is a schematic view sequentially showing steps of a method ofmanufacturing an exemplary hollow drive shaft for a vehicle according tothe present invention.

FIG. 5 and FIG. 6 are graphs showing change in physical propertiesduring a swaging process of a hollow tube used when the exemplary hollowdrive shaft according to the present invention is manufactured.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the present invention as disclosed herein,including, for example, specific dimensions, orientations, locations,and shapes will be determined in part by the particular intendedapplication and use environment.

DETAILED DESCRIPTION

Reference will now be made in detail to various embodiments of thepresent invention(s), examples of which are illustrated in theaccompanying drawings and described below. While the invention(s) willbe described in conjunction with exemplary embodiments, it will beunderstood that the present description is not intended to limit theinvention(s) to those exemplary embodiments. On the contrary, theinvention(s) is/are intended to cover not only the exemplaryembodiments, but also various alternatives, modifications, equivalentsand other embodiments, which may be included within the spirit and scopeof the invention as defined by the appended claims.

As shown in FIG. 2, a hollow drive shaft according to the presentinvention includes a hollow shaft 10 having therein a hollow portion 16that extends along a rotation axis, and first and second stems 20 and 30joined to left and right sides of the hollow shaft 10.

The hollow shaft 10 is made by assembling two hollow tubes 12 and 14machined to have different characteristics with each other. One of thefirst hollow tube 12 and the second hollow tube 14 having the samediameter is compressed by a swaging process to reduce an outer diameterthereof, and then is inserted into the other hollow tube.

Each of the first and second hollow tubes 12 and 14 is a hollow bodyhaving a circular cross-section, and is of a cylindrical structure thathas, in a central portion thereof, the hollow portion 16 extending alongthe rotation axis and that is open at both ends thereof.

Further, the first and second sterns 20 and 30 are joined to both endsof the hollow shaft 10 by a friction welding method that performspressure welding using frictional heat generated when welded parts(hollow shaft and stems) rotate relative to each other.

Each of the first and second stems 20 and 30 is a hollow body or anon-hollow body having an approximate circular cross-section, and is ofa hollow shape that has a hollow portion extending along the rotationaxis, or a solid shape that has no hollow portion. As shown in FIG. 2,in the case of the non-hollow body, hollow portions 22 and 32 which arepartially concave are provided on an end of the non-hollow bodyconnected to the hollow shaft 10.

Hereinafter, the method of manufacturing the hollow drive shaftconfigured as such will be described with reference to FIGS. 3 and 4.

First, the method of manufacturing the hollow drive shaft according tovarious embodiments of the present invention will be described withreference to FIG. 3.

As shown in FIG. 3, the first and second hollow tubes 12 and 14 havingthe same diameter are fabricated and prepared, and then the first andsecond stems 20 and 30 are fabricated and prepared. One of the first andsecond hollow tubes 12 and 14 is compressed by swaging to reduce theouter diameter thereof, and then is inserted into the other hollow tube.

In the manufacturing method shown in FIG. 3, the second hollow tube 14is subjected to swaging such that the outer diameter of the secondhollow tube 14 is less than the inner diameter of the first hollow tube12. Accordingly, the diameter of the second hollow tube 14 is reducedand then the second hollow tube 14 is inserted into the first hollowtube 12.

Although not shown in the drawings, before or after the second hollowtube 14 is inserted into the first hollow tube 12, torsion torque may beapplied to the first and second hollow tubes 12 and 14 in the samedirection and, thus each of the hollow tubes 12 and 24 may be twisted.

Here, the first and second hollow tubes 12 and 14 and the first andsecond stems 20 and 30 are generally made of a material used when thehollow drive shaft is manufactured.

After the second hollow tube 14 is inserted into the first hollow tube12 to manufacture the hollow shaft, the first stem 20 and the secondstem 30 are joined to the left and right sides of the hollow shaft 10,respectively, by friction welding using frictional heat, so that thehollow drive shaft is manufactured.

In the hollow drive shaft manufactured as such, the physical properties(strength and the like) of the second hollow tube 14 are increased byswaging. Thus, if it has the same thickness as the conventional hollowshaft, performance such as a torsion rigidity ratio and a naturalfrequency is increased. Consequently, in comparison with theconventional hollow drive shaft having the same performance, a size anda weight may be reduced, so that fuel efficiency may be enhanced due toa reduction in weight and it is more advantageous in terms of layout.

In addition, when the hollow drive shaft manufactured as such is appliedto the internal-combustion-engine vehicle driven under theunidirectional movement condition, the effect of improving durabilitymay be obtained under the unidirectional movement condition where thetorsion torque is applied to the drive shaft only in the forwardmovement direction of the vehicle.

Next, a method of manufacturing a hollow drive shaft according tovarious embodiments of the present invention will be described withreference to FIG. 4.

As shown in FIG. 4, the first and second hollow tubes 12 and 14 havingthe same diameter are fabricated and prepared, and the first and secondstems 20 and 30 are fabricated and prepared. Subsequently, the secondhollow tube 14 is subjected to swaging so that the outer diameter of thesecond hollow tube 14 is less than the inner diameter of the firsthollow tube 12, and consequently the diameter of the second hollow tube14 is reduced.

Further, torsion torque is applied to the first and second hollow tubes12 and 14 in different directions, so that the first and second hollowtubes 12 and 14 are twisted in different directions.

For example, torsion torque is applied to the first hollow tube 12clockwise, so that it is twisted clockwise. In contrast, torsion torqueis applied to the second hollow tube 14 counterclockwise, so that it istwisted counterclockwise.

The first and second hollow tubes 12 and 14 are twisted in differentdirections by applying the torsion torque so that durability against areverse external force resulting from the residual stress of the firstand second hollow tubes 12 and 14 is enhanced.

Although not shown in the drawings, it is possible to apply torsiontorque to one of the first and second hollow tubes 12 and 14 to betwisted.

After the second hollow tube 14 is inserted into the first hollow tube12 to make the hollow shaft 10, the first and second stems 20 and 30 arejoined to the left and right sides of the hollow shaft 10 throughfriction welding, thereby manufacturing the hollow drive shaft.

Although not shown in the drawings, after the second hollow tube 14 isinserted into the first hollow tube 12 to make the hollow shaft 10, itis possible to apply torsion torque to the first and second hollow tubes12 and 14, which are assembled with each other, in different directions.

Even in this case, it is possible to apply torsion torque to one of thefirst and second hollow tubes 12 and 14 to be twisted.

Further, when torsion torque is applied to the cylindrical hollow tubes12 and 14, for example, in the state where one end of the hollow tubes12 and 14 is fixedly supported, torsion torque is applied to the otherend of the hollow tubes 12 and 14 by rotating it in one direction to betwisted in one direction.

Here, since the cylindrical hollow tubes 12 and 14 formed to be twistedby applying torsion torque thereto is known to those skilled in the art,a detailed description thereof will be omitted.

The hollow drive shaft manufactured in this way previously impartstorsion torques of different directions to the first and second hollowtubes 12 and 14 constituting the hollow shaft 10, thereby increasingdurability against external force in the bidirectional-movementcondition of the vehicle. Therefore, the invention may reduce the sizeand weight of the hollow drive shaft compared to the conventional hollowdrive shaft having the same durability. As a result, fuel efficiency isenhanced due to the lightness of the hollow drive shaft, and besides thehollow drive shaft of this invention is more advantageous in terms oflayout.

In addition, when the hollow drive shaft manufactured as such is appliedto an internal-combustion-engine vehicle driven under the unidirectionalmovement condition, durability may be enhanced under the unidirectionalmovement condition where torsion torque is applied to the drive shaftmainly in a forward direction. Moreover, when the hollow drive shaft ofthis invention is applied to an eco-friendly vehicle driven under thebidirectional-movement condition by regenerative braking, such as ahybrid vehicle or an electric vehicle, durability may be enhanced underthe bidirectional-movement condition where torsion torque is applied tothe drive shaft in both a forward direction and a rearward direction.

As described above, the hollow drive shaft according to the presentinvention employs a structure obtained by swaging the hollow tubeshaving the same diameter as necessary and applying torsion torquethereto regardless of the unidirectional movement condition and thebidirectional-movement condition of the vehicle. Therefore, when thehollow drive shaft of the invention is applied to the eco-friendlyvehicle as in the conventional hollow drive shaft, it is unnecessary toadditionally make a hollow shaft material that is increased in thicknessto cope with the bidirectional-movement condition of the vehicle.

Meanwhile, FIGS. 5 and 6 are graphs showing change in physicalproperties when the hollow tube used to make the hollow drive shaftaccording to the present invention is subjected to swaging.

As shown in FIG. 5, when the hollow tube made of a micro-alloyed steelmaterial is subjected to swaging, it is seen that the higher asectional-area reduction ratio of the hollow tube is, the higher surfacehardness of the hollow tube is.

Further, as shown in FIG. 6, after the hollow tube made of themicro-alloyed steel material is subjected to swaging, it is seen thatradial hardness of the hollow tube is increased.

Thus, when the hollow tube having a circular cross-section is subjectedto swaging, it is seen that, as the sectional-area reduction ratio ofthe hollow tube is increased, maximum tensile strength and hardness arelinearly increased.

As described above, the present invention provides a hollow drive shaftfor a vehicle and a manufacturing method thereof, which are enhanced inbidirectional-movement durability to cope with thebidirectional-movement condition of an eco-friendly vehicle withoutincreasing the size of the drive shaft, thereby being applicable to bothan internal-combustion-engine vehicle and an eco-friendly vehicle, andwhich are more advantageous in layout compared to a conventional hollowdrive shaft having equivalent performance by increasing a size, therebybeing applicable to even a vehicle to which the hollow drive shaftcannot be applied because of a problem concerning layout such as spacingbetween the drive shaft and peripheral parts.

For convenience in explanation and accurate definition in the appendedclaims, the terms “upper” or lower, “inner” or “outer” and etc. are usedto describe features of the exemplary embodiments with reference to thepositions of such features as displayed in the figures.

The foregoing descriptions of specific exemplary embodiments of thepresent invention have been presented for purposes of illustration anddescription. They are not intended to be exhaustive or to limit theinvention to the precise forms disclosed, and obviously manymodifications and variations are possible in light of the aboveteachings. The exemplary embodiments were chosen and described in orderto explain certain principles of the invention and their practicalapplication, to thereby enable others skilled in the art to make andutilize various exemplary embodiments of the present invention, as wellas various alternatives and modifications thereof. It is intended thatthe scope of the invention be defined by the Claims appended hereto andtheir equivalents.

1-7. (canceled)
 8. A hollow drive shaft for a vehicle, comprising: a hollow shaft; and first and second stems joined to left and right sides of the hollow shaft, wherein the hollow shaft is configured such that one of a first hollow tube and a second hollow tube is inserted into a remaining hollow tube of the first hollow tube and the second hollow tube.
 9. The hollow drive shaft of claim 8, wherein the hollow shaft is formed by reducing an outer diameter of one of the first and second hollow tubes having a same diameter through swaging, and then inserting the hollow tube having the reduced outer diameter into the remaining hollow tube.
 10. The hollow drive shaft of claim 8, wherein one of the first and second hollow tubes is subjected to swaging, such that an outer diameter thereof is reduced to be less than an inner diameter of the remaining hollow tube, and then torsion torque is applied to the first and second hollow tubes, respectively, in different directions to be twisted.
 11. The hollow drive shaft of claim 8, wherein the hollow shaft has therein a hollow portion extending along a rotation axis, each of the first and second stems having a solid shape having no hollow portion therein or having a hollow shape that extends along the rotation axis. 